yeah, 2wd doesn't have a transfer case. what you slid the drive shift yoke into, which I guess is where you replaced the seal is called the tail housing. it's part of the transmission.
a transfer case looks much different but it does bolt to the tranny in the same place as the tail housing does. it's just much larger, goes off the drivers side of the truck. and has its own fluid inside it. the tail housing doesn't. it's just a empty kinda cone shape aluminum housing straight back from the tranny.
so if it was leaking from the front of the drive shaft where it goes into the transmission. that's transmission fluid. dex 6. if it was the rear end housing, where the drive shaft bolts into the rear axle housing that was leaking. that's gear lube. 75-90w I believe. definitely don't mix those to up and put the wrong fluid in either one.